The present invention relates to a rotary assembly comprising a stator and a rotor of axis .DELTA., rotary drive means, radial support means, and an active magnetic axial abutment comprising a magnetic circuit in two portions, namely a fixed portion secured to the stator, and a moving portion secured to the rotor, the two portions being separated from each other by two parallel plane air gaps, each portion of said magnetic circuit being circularly symmetrical about axis .DELTA., and having the shape of an open channel-section extending about said axis .DELTA., the ends of each portion of the magnetic circuit forming two plane surfaces constituting two concentric circular bands centered on the axis .DELTA., and perpendicular thereto, the open ends of the two portions of magnetic circuit facing each other, an electrical axial abutment coil being received in the inside annular space of the fixed portion of said magnetic circuit.
The invention is particularly applicable to vacuum pumps such as turbomolecular blade pumps of the Holweck type.